15A NCAC 02T .1005       DESIGN CRITERIA

(a)  Design criteria related to closed-loop recycle systems in general.

(1)           There shall be no public access to the wastewater treatment equipment, wastewater storage structures or to the wastewater within a closed-loop recycle facility.

(2)           Where potable water is used to supplement a closed-loop recycle water system, there shall be an air gap separation between the potable water and closed-loop recycle water systems.

(b)  Design criteria related to treatment and storage units utilized in closed-loop recycle systems.

(1)           The facility shall have the ability to stop production of effluent, return the effluent back to the treatment facility, store the effluent, or discharge the effluent to another permitted wastewater treatment facility when recycling can not be conducted.

(2)           Essential treatment units shall be provided in duplicate where proper operation of the treatment unit is essential to the operation of the closed-loop recycle system and the operation can not safely or efficiently be immediately stopped or altered to operate without the closed-loop recycle system.

(3)           An automatically activated standby power source, system shutdown, or other means shall be employed to prevent improperly treated wastewater from entering a treated waste water storage structure or from being recycled where loss of power would create an unsafe condition.

(4)           Where they are suitable for reuse, residues recovered during the treatment process may be recycled through the processes that generated the wastewater rather than disposed of as a waste.

(5)           A water tight seal on all treatment/storage units or a minimum of two feet protection from the 100-year flood shall be provided.

(6)           Storage units in a closed-loop recycle system shall be designed to contain the accumulation of water from a 25-year, 24-hour storm event with 1 foot freeboard, unless the system is protected from rainfall and runoff.

(7)           The bottoms of earthen impoundments, trenches or other similar excavations shall be at least four feet above the bedrock surface, except that the bottom of excavations which are less than four feet above bedrock shall have a liner with a hydraulic conductivity no greater than 1 x 10-7 centimeters per second.  Liner thickness shall be that thickness necessary to achieve a leakage rate consistent with the sensitivity of classified groundwaters.  Liner requirements may be reduced if it can be demonstrated by predictive calculations or modeling methods acceptable to the Director that construction and use of these treatment and disposal units will not result in contravention of surface water or groundwater standards.

(8)           Treatment works and disposal systems utilizing earthen basins, lagoons, ponds or trenches, excluding holding ponds containing non-industrial treated effluent prior to spray irrigation, for treatment, storage or disposal shall have either a liner of natural material at least one foot in thickness and having a hydraulic conductivity of no greater than 1 x 10-6 centimeters per second when compacted, or a synthetic liner of sufficient thickness to exhibit structural integrity and an effective hydraulic conductivity no greater than that of the natural material liner.


History Note:        Authority G.S. 143-215.1; 143-215.3(a);

Eff. September 1, 2006.